Minority-Spin Impurity Band in n-Type (In,Fe)As: A Materials Perspective for Ferromagnetic Semiconductors

TL;DR

This study uses SX-ARPES to reveal the band structure of n-type (In,Fe)As, showing a minority-spin Fe-3d impurity band near the conduction band minimum that influences ferromagnetism.

Contribution

It provides direct experimental evidence of the minority-spin impurity band and its hybridization with the conduction band, offering new insights into carrier-induced ferromagnetism in n-type FMSs.

Findings

Identification of a minority-spin Fe-3d impurity band below the conduction band minimum.

Observation of hybridization between Fe-3d states and InAs conduction band.

Band structure variation with band filling suggests a non-rigid-band behavior.

Abstract

Fully understanding the properties of n-type ferromagnetic semiconductors (FMSs), complementary to the mainstream p-type ones, is a challenging goal in semiconductor spintronics because ferromagnetism in n-type FMSs is theoretically non-trivial. Soft-x-ray angle-resolved photoemission spectroscopy (SX-ARPES) is a powerful approach to examine the mechanism of carrier-induced ferromagnetism in FMSs. Here our SX-ARPES study on the prototypical n-type FMS (In,Fe)As reveals the entire band structure including the Fe-3d impurity bands (IBs) and the host InAs ones, and provides direct evidence for electron occupation of the InAs-derived conduction band (CB). A minority-spin Fe-3d IB is found to be located just below the conduction-band minimum (CBM). The IB is formed by the hybridization of the unoccupied Fe-3d states with the occupied CBM of InAs in a spin-dependent way, resulting in the large spin polarization of CB. The band structure with the IB is varied with band filling, which cannot be explained by the rigid-band picture, suggesting a unified picture for realization of carrier-induced ferromagnetism in FMS materials.